Which microbes are motile

Cell shape contributes to this. Spherical cells have a torque towards the surface that induces spin but does not cause hydrodynamic entrapment. Rod-shaped cells have the same surface-induced torque, but also have a balancing form-induced drag. The two torques cause hydrodynamic entrapment and result in rod-shaped cells swimming parallel to the surface Vigeant et al.

The aspect ratio of the cell determines whether the torques balance, so cell shape is one determinant of how motile cells react to surfaces. Chemla used a superconduction quantum interference device to study bacterial magnetotaxis. Remarkably, they created a microscope of magnetic fields of similar strength to the magnetic field of the Earth.

They measured an average flagellar rotation rate of Using nonmotile cells, they were able to measure the rotational drag coefficient, the average cell size and distribution around that average. These measurements are impossible to make simultaneously on 10— million cells by light microscopy. The authors claim nonmagnetotactic motility can be analysed by attaching magnetic particles to cells. New techniques are only one way to advance motility research.

Flagellar shape and bundle stress are known to respond to environmental change Calladine, , but new varieties of flagellar control continue to be discovered. The complex flagellar filament of Rhizobium lupini is one new variant Scharf, This consists of three flagellin subunits connected by interflagellin bonds that lock in a right-handed helical conformation.

This is critical for flagella that only rotate clockwise and that tumble because of asynchronous deceleration of the bundled filaments. The filaments are stable from pH 4 to 9, but straighten at more extreme pH and at high viscosity.

Scharf proposes that this response prevents motor stalling. It is unknown if locked flagella perform direct viscotaxis or pH taxis. However, changes in these conditions make tumbling more frequent.

Orientation control by speed modulation of a single conformationally dynamic flagellum was described in Rhodobacter sphaeroides Armitage et al. Initially, R. It may be an unlikely strategy for any species because it is useful only for cells within a few hundredths of a micrometre of 0. In any case, the observation of turning with conformationally dynamic flagella and the report that R. Modelling suggests that flagellar bundle integrity is influenced by individual flagella creating turbulent wakes Trachtenberg et al.

This is surprising because bacteria and their flagella are the ultimate noninertial, laminar-flow-only devices. Usually, flow is laminar for Reynolds numbers less than 1 and fully turbulent over In contrast, R. The sharp-edged flagella and the Archimedean-screw-like contours are claimed to produce turbulence at a Reynolds number of 0. Experimental verification of this seemingly unlikely theoretical work would alter microfluidics and cause a paradigm shift in fluid mechanics.

The full implications of flagella-generated turbulence are unclear; but the consequences of speed variation are clear in some species. Rhodobacter sphaeroides shows a variety of swimming behaviours within and between individual cells Armitage et al.

Speeds were constant, oscillating or intermittent. The intermittent behaviour combines the other two behaviours, where speed is high with occasional sharp, short-duration drops. Similarly, starting could be immediate or a slow acceleration, occurring over milliseconds to seconds. A single cell may use all combinations. Flagellar conformation changes over the same timescale as speed Armitage et al.

This correlative link is supported by the mechanistic consistency of flagellar changes that are a tight, high-amplitude coil that does not propel the cell, a helix that propels the cell and a straight form that propels the cell.

Transition states exist that are curled at the end and straight at the base. The transition and coiled states reorient the cell and represent distinct rotation speeds. Thus, fine motor control is important to environmental bacteria. The flagellar motor is 45 nm and embedded in the cytoplasmic membrane. The motors of the commonly investigated bacteria Bacillus subtilis, E. The alkaline pH of seawater makes establishing an inwardly directed proton gradient difficult.

Motor components continue to be investigated. They form a transmembrane proton channel anchored to a peptidoglycan layer. These latter flagella are synthesized when the cells are on the surface or in viscous environments.

The result is a swarming morphotype, presumably used for movement along marine animals and other surfaces. Vibrio alginolyticus has a similar system Kawagishi et al. The marine Halomonas sp. Although more work is necessary, the dual system in Halomonas may give them functional versatility.

Laser dark-field microscopy shows that E. Swimming speeds are a linear function of the flagellar rotation speed for V. Motor rotation can be controlled by chemicals that reduce the proton gradient across the membrane Minamino et al. The high pH and low organic matter concentration of seawater may contribute to the high speeds of marine bacteria Mitchell et al.

Alternatively, the Aer gene products sense intracellular energy levels rather than specific chemicals in the external environment Rebbapragada et al. This allows the energy available in the cell to be maximized through movement, without having to have an extensive detection and processing system for each metabolizable type of molecule.

Similarly, sensitivity is enhanced by chemoreceptors that work in teams by forming clusters at the poles of the cell Ames et al. The grouped receptors were the first clue that body-length detection was possible.

For small, free-swimming bacteria, spatial comparison over a body length is more sensitive than temporal comparison Dusenbery, The theoretical lower size limits are 0. The currently unanswered challenge for experimentalists is to measure the lower size limits in real bacteria for spatial and temporal chemical detection.

Whether spatial or temporal sensing is more advantageous depends on the molecule and gradient length. There are established predictions for ammonium, iron and many other compounds Dusenbery, , but experimental confirmation is needed and would provide insight into sediment bacterial distributions and migrations.

These vibroid-shaped bacteria are remarkable because they progress along their short axis. The movement is propeller-like, but the rotation is not driven by a central shaft, rather by flagella at the ends of the cell. Flagellar bundle rotation speed is proportional to the ambient oxygen concentration, which causes U-shaped tracks, a few hundred micrometres long and helical klinotaxis.

This is true chemotaxis, where the swimming direction and gradient correlate. In stable gradients, temporary attachment by mucous threads is used for maintaining position. This intermittent attachment presumably reduces the expense of motility and highlights the value of motility in finding unusual species in microniches.

The behaviour was described before the cells were identified or cultured, but clearly the results provide an incentive to investigate other components of its microbiology as well as looking for other bacteria that sense gradients over their body length.

Ultimately, the function of cell components needs to be viewed in terms of behaviour in individual bacteria. For E.

For example, it is assumed that motility must be chemotactic to be useful. However, Merrell showed that hyperinfectious cholera bacteria in the intestine are highly motile, but the chemotaxis genes are repressed, which uncouples motility and chemotaxis, reducing retention time in the intestine, and increasing the likelihood of the infection spreading.

Uncoupling motility from chemotaxis is a simple alteration. For other species, the alteration and behavioural changes are complex. Photorhabdus temperata is mutalistic with pathogenic nematodes of the Heterorhabditis genus. The bacteria have primary and secondary forms that prefer oxic and anoxic environments. The primary form is motile in both environments, but the secondary form is motile under anoxic conditions Hodgson et al.

This may reflect differences in culture conditions, strain variation and history. When the secondary form is transferred from anoxic to oxic conditions it remains motile, indicating that, once initiated, motility is maintained in a cell Hodgson et al. Cells are nonmotile without sodium, but potassium and magnesium substitute for sodium with speeds reduced marginally in the primary form and marginally by potassium and by about two-thirds for magnesium in the secondary form.

This is at 75 mM. Between and mM concentrations of potassium and magnesium, the motility decreases Hodgson et al.

A uniform response might be expected for organic signal molecules that are useful as sources of energy and cellular building blocks. However, E. It is unknown whether an intermediate concentration change exists where there is no response. The biphasic response arises from double signals with the Tar receptor, signalling attraction, and the Tsr receptor, signalling repulsion.

Biphasic responses are important to consider where motility is investigated in a large number of species Johansen et al. Johansen measured motility in 84 species and strains of marine bacteria. Run times ranged from 0. The extremes were from unsequenced isolates, but it was unreported whether they were recent isolates. Swimming speed decreases with increasing nutrient concentration Mitchell et al.

The implications for interpretation of the results are unclear because nutrient sensitivity was not examined and the automatic tracking system only measured a subset of the possible bacterial speeds and turning angles.

The work does show the diversity of motile marine bacteria. Methods for testing the limits of bacterial motility are needed if differences and extremes in motility are to be discovered.

Niche position may be useful for the assessment of motility. Schmitt emphasizes that E. Sinorhizobium meliloti shows a more diverse chemotaxis system than E. Types of flagellar filaments and their rotation differ between species. Sinorhizobium meliloti has a stiff right-handed filament for viscous swimming. Escherichia coli has monomeric flagellin subunits, whereas S. The latter creates three locking, helical ribbons causing flagella to only rotate clockwise and orientational control to be by rotation rate modulation.

Thus, S. For S. The speed control mechanisms are unknown. The importance of behavioural repertoire is becoming clear. Vibrio fischeri , a species symbiotic with the bobtail squid, is chemotactic to N -acetylneuraminic acid NANA , nucleosides and nucleotides, but not to the individual components of these compounds DeLoney et al.

Chemotaxis and respiration of thymidine in this species shows the difficulty in estimating growth by thymidine incorporation. Chemotaxis to, and metabolism of, NANA is consistent with taxis to squid, as it is produced by squid surfaces. Nucleotides and nucleosides are released during the apoptosis of symbiosis. The mechanisms are unknown. The number of chemoreceptor genes are unknown for Flavimonas oryzihabitans , but this bacterium is chemotactic to gas, oil and hexadecane, and its chemoreceptors might be as diverse as those in V.

There was minimal microscopic description in this study. This describes run and reverse chemotaxis, possibly a new variant. Chemotaxis was also reported towards detergents and oxygen in the negative controls, which suggests the chemotaxis was not to an alkane, but to the energy state.

Energy state sensing may be common in chemotaxis. Aer and Tsr receptors are independent but redundant and probably universal in containing a PAS domain Stock, This emphasizes the importance of aerotaxis. There is a trade-off between sampling and sensitivity Johansen et al. The limits for each are unclear, but experiments suggest that most bacteria are far from those limits. This indicates long-term response dynamics and represents a new research area. Direction-specific reversing and circular orbits are new behaviours and indicate new control mechanisms.

There appear to be at least seven distinct motility patterns. In addition to the classical run and tumble chemotaxis, bacteria are capable of run and reverse, steering, localizing, tracking, orbiting, and run and stop Fig. Steering and localization are the only nonmigratory behaviours. Reorientation is by tumbling, reversing or steering. Movement patterns for motile bacteria. The dotted line indicates that this method, while previously attributed to Rhodobacter spheroides , is currently not reported for any bacterial species.

Increasing dark grey shading indicates increasing attractant concentration. The energetic cost of individual movement patterns can be calculated. Combining size, run length and the minimum chemotactic cost for each movement pattern shows where those patterns are most cost effective Fig.

The model indicates that all moving organisms follow one universal law Fig. Bacteria have to make physical contact with host cells before they can adhere to those cells and resist being flushed out of the body.

Motile bacteria can use their flagella and chemotaxis to swim through mucus towards mucosal epithelial cells. Because of their thinness, their internal flagella axial filaments , their corkscrew shape, and their motility, certain spirochetes are more readily able enter lymph vessels and blood vessels and spread to other body sites.

Many bacteria produce enzymes that degrade the extracellular matrix proteins that surround cells and tissues and help to localize infection, making it easier for those bacteria to spread within the body. Some bacteria produce toxins that induce diarrhea in the host enabling the pathogen to more readily leave one host and enter new hosts through the fecal-oral route.

Learning Objectives State why it might be of an advantage for a bacterium trying to colonize the bladder or the intestines to be motile. Describe specifically how certain bacteria are able to use motility to contact host cells and state how this can promote colonization.

Briefly describe why being extremely thin and being motile by means of axial filaments may be an advantage to pathogenic spirochetes.

Give one example of how a nonmotile bacterium may be able to better disseminate within a host. Give a brief description of how a bacterium may use toxins to better disseminate from one host to another. Highlighted Bacterium Read the description of Helicobacter pylori and match the bacterium with the description of the organism and the infection it causes. Summary Bacteria have to make physical contact with host cells before they can adhere to those cells and resist being flushed out of the body.

Nan, B. Bacteria that glide with helical tracks. Lapidus, I. Gliding motility of Cytophaga sp. Helical flow of surface protein required for bacterial gliding motility. This study shows that surface adhesins that enable gliding motility in F. Shrivastava, A. The screw-like movement of a gliding bacterium is powered by spiral motion of cell-surface adhesins.

Braun, T. Flavobacterium johnsoniae gliding motility genes identified by mariner mutagenesis. Flavobacterium johnsoniae GldJ is a lipoprotein that is required for gliding motility. Nelson, S. Flavobacterium johnsoniae SprA is a cell surface protein involved in gliding motility. Lauber, F. Type 9 secretion system structures reveal a new protein transport mechanism. Nature , 77—82 Pate, J. Evidence that gliding motility in prokaryotic cells is driven by rotary assemblies in the cell envelopes.

A rotary motor drives Flavobacterium gliding. This study provides evidence that gliding motility of Bacteriodetes is powered by a rotary molecular motor. A molecular rack and pinion actuates a cell-surface adhesin and enables bacterial gliding motility. This study combines biophysical experiments with fluorescence imaging to propose a mechanistic model for gliding motility. Gorasia, D. Leone, P. Islam, S. The mysterious nature of bacterial surface gliding motility: a focal adhesion-based mechanism in Myxococcus xanthus.

Cell Dev. Novel mechanisms power bacterial gliding motility. Sun, M. Motor-driven intracellular transport powers bacterial gliding motility. Myxobacteria gliding motility requires cytoskeleton rotation powered by proton motive force.

Faure, L. The mechanism of force transmission at bacterial focal adhesion complexes. By tracking the components of the M.

Fu, G. MotAB-like machinery drives the movement of MreB filaments during bacterial gliding motility. CglB adhesins secreted at bacterial focal adhesions mediate gliding motility.

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Matsuyama, T. Mutational analysis of flagellum-independent surface spreading of Serratia marcescens on a low-agar medium. Shrout, J. A fantastic voyage for sliding bacteria. Lauga, E. The hydrodynamics of swimming microorganisms. Schuech, R. Motile curved bacteria are Pareto-optimal. How bacteria swim. Milne, J. Cryo-electron microscopy—a primer for the non-microscopist. FEBS J. Egelman, E. The current revolution in cryo-EM. Download references. The authors thank K.

Fahrner for critical reading of the manuscript. You can also search for this author in PubMed Google Scholar. Correspondence to Navish Wadhwa or Howard C. Nature Reviews Microbiology thanks W. Durham, who co-reviewed with J. Wheeler, D.

Kearns and the other, anonymous, reviewer s for their contribution to the peer review of this work. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

A dimensionless parameter in the equations of motion of fluids that indicates the relative importance of inertial forces, forces that accelerate fluids and viscous forces, which shear fluids. Movement across surfaces that occurs when thin filaments are extended outwards from the cell, stick to the substratum at their distal tips and then are disassembled at their base.

Movement across surfaces that occurs when adhesins, driven along tracks fixed to the cell wall, adhere to the substratum. Long, thin and rigid components of the bacterial flagellum, subject to changes in crystal polymorphic form which, when rotated at their base, generate thrust that pushes the cell forward.

Groups of flagellar filaments rotating in parallel that push a peritrichously flagellated cell forward. Flagellation with filaments that appear at one or the other pole: monotrichous, single filaments; lophotrichous, a tuft of filaments. Random motion of an object suspended in a fluid caused by collisions with the molecules of the fluid. A behavioural response to chemical gradients whereby cells move towards regions that contain more nutrients or nutrient homologues and away from noxious regions.

Migration by stepping in directions chosen at random. The walk is biased if steps in a particular direction are longer or more frequent. Cells fixed to glass by a single flagellar filament and, instead of rotating the flagellar filament, the motor rotates the cell body. Also known as force-generating units, torque-generating units or MotA—MotB complexes, an assembly of five MotA proteins and two MotB proteins supporting two transmembrane ion channels that powers flagellar rotation.

The electrochemical gradient of protons across a membrane due to a combination of the membrane potential and the concentration gradient of protons.

Protons driven down this electrochemical gradient energize various cellular processes, including flagellar rotation, ATP synthesis and ion transport. Water has a relatively small viscosity, molasses has a relatively large viscosity. A fluid in which the viscosity does not depend on the rate of shear for example, water and solutions of Ficoll.

Solutions containing long unbranched chains, such as mucus, hyaluronic acid, methyl cellulose or polyvinylpyrrolidone, are not Newtonian fluids.

Small organic compounds that are synthesized by the cell to affect intracellular or extracellular osmolarity. Compounds that when added to a liquid lower its surface tension.

Soap and detergent are common examples. The tendency of liquid surfaces to minimize the surface area and resist extension. Liquids with lower surface tension spread more easily. Reprints and Permissions. Bacterial motility: machinery and mechanisms. Nat Rev Microbiol Download citation. Accepted : 10 August Published : 21 September Anyone you share the following link with will be able to read this content:.

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Abstract Bacteria have developed a large array of motility mechanisms to exploit available resources and environments. Access through your institution. Buy or subscribe. In addition to characterizing the ensemble behavior of the bacteria, we have observed a gallery of distinct trajectories of individual swimmers on and near fluid interfaces.

We attribute these diverse swimming behaviors to differing trapped states for the bacteria in the fluid interface. These trajectory types include Brownian diffusive paths for passive adsorbed bacteria, curvilinear trajectories including curly paths with radii of curvature larger than the cell body length, and rapid pirouette motions with radii of curvature comparable to the cell body length.

Finally, we see interfacial visitors that come and go from the interfacial plane. We characterize these individual swimmer motions. This work may impact nutrient cycles for bacteria on or near interfaces in nature.

This work will also have implications in microrobotics, as active colloids in general and bacteria in particular are used to carry cargo in this burgeoning field. Finally, these results have implications in engineering of active surfaces that exploit interfacially trapped self-propelled colloids. Interfacial visitor bacterium I AVI. Immotile bacterium moving via Brownian diffusion bacterium AVI.

Bacterium with a pirouette motion AVI. Bacterium swimming in a curly path AVI. Such files may be downloaded by article for research use if there is a public use license linked to the relevant article, that license may permit other uses. View the notice. More by Jiayi Deng. More by Mehdi Molaei. More by Nicholas G.